1. Field of the Invention
The present invention relates to a data communication apparatus, a communication system switching method and a memory medium, and more particularly it relates to a data communication apparatus including analogue terminal communication means for effecting communication with an analogue terminal and data communication network connecting means for effecting connection to a data communication network, a communication system switching method applied to such a data communication apparatus, and a memory medium storing a program for executing such a communication system switching method.
2. Related Background Art
Recently, data communication utilizing internets has been progressed remarkably.
There have been proposed ITU recommendation H.323 for effecting real time communication of video data or voice data by utilizing an internet and ITU recommendation T.38 for effecting real time facsimile communication by utilizing an internet. Further, ITU recommendation T.37 in which facsimile data is converted into a TIFF file which is in turn sent through an E-mail has also been proposed. In apparatus utilizing such techniques, the communication can be realized via the internet inexpensively. In the ITU recommendation T.38 , since a sending terminal directly performs sending/receiving of data with respect to a terminal which ultimately receives the data, transmission of data can be recognized at real time.
FIG. 4 shows an example of a construction of a conventional communication system based on the ITU recommendation T.38 for effecting real time facsimile communication by utilizing the internet.
In FIG. 4, the system includes an Internet 101, a sender facsimile apparatus 102, a receiver facsimile apparatus 103, a sender gateway (GW) 104 and a receiver GW 105. The sender GW 104 and the receiver GW 105 are connected to the internet 101 to effect data communication through the internet 101. Further, the sender facsimile apparatus 102 and the receiver facsimile apparatus 103 are generally used G3 facsimile apparatuses, which are generally connected to analogue public networks (PSTN) 106, 107, respectively to effect facsimile sending or facsimile receiving of image information. The sender facsimile apparatus 102 is connected to the sender GW 104 via the PSTN 106 and the receiver facsimile apparatus 103 is connected to the receiver GW 105 via the PSTN 107, so that real time internet facsimile communication of the image information can be performed from the sender facsimile apparatus 102 to the receiver facsimile apparatus 103 through the sender GW 104, internet 101 and receiver GW 105.
FIG. 5 is a view showing a communication sequence performed when the image information is sent from the sender facsimile apparatus 102 to the receiver facsimile apparatus 103 in the conventional communication system shown in FIG. 4.
First of all, the sender facsimile apparatus 102 effects off-hook and dial operation to call out the sender GW 104. The sender GW 104 detects the call-out and responds thereto. When the off-hook is established, the sender GW 104 is connected to the sender facsimile apparatus 102 as the analogue terminal via the PSTN 106 (step 110).
The sender GW 104 designates a receiver GW 105 connected to the internet 101 and sends data packet comprised of a call establishment signal to the designated receiver GW 105 through the internet 101 (step 111). The call establishment signal includes information for designating a receiver facsimile apparatus 103 as a facsimile recipient. When the receiver GW 105 receives the call establishment signal packet, the receiver GW 105 designates the receiver facsimile apparatus 103 and connects thereto (step 112). The receiver GW 105 detects such connection and sends the data packet comprised of the call establishment signal to the sender GW 104 through the internet 101 (step 113). By such a sequence, the sender GW 104 and the receiver GW 105 connects a FAX channel therebetween through the internet 101 (step 114), so that an operation of T.38 session defined by the ITU T.38 is permitted in the sender facsimile apparatus 102, sender GW 104, receiver GW 105 and receiver facsimile apparatus 103 (step 115) and the image information can be sent from the sender facsimile apparatus 102 to the receiver facsimile apparatus 103.
When the facsimile sending operation is finished, since the sender facsimile apparatus 102 effects an on hook operation, the sender GW 104 detects such operation and effects disconnection from the sender facsimile apparatus 102 (step 116) and further sends data packet comprised of a release completion signal to the receiver GW 105 through the internet 101 (step 117). When the release completion signal packet is received, the receiver GW 105 sends busy tone to the receiver facsimile apparatus 103 (step 118), and the receiver facsimile apparatus 103 effects the on-hook operation accordingly (step 119).
In this way, the sequence of the real time internet facsimile communication is ended.
In the gateway (GW) for effecting the communication by the real time system (T.38), since the communication system is fixed and is not flexible, for example, a service such as the ITU recommendation T.37 in which the data of facsimile original is developed as the TIFF file which is in turn sent through the E-mail cannot be utilized.